linux awk - awk tutorial

【基本介绍】
awk是一款强大的对文件内容进行处理的软件，可以当作是一个脚本语言。
这里列出大概的学习框架和简单例子。


【学习列表】
1.Built-in functions for numeric operations
2.Built-in functions for String operations
3.Build-in functions for input output operations
4.awk if statement(if,if else,if else if,:?)
5.awk loops(do while,for loop,break,continue,exit)
6.Build-in variables(FS,OFS,RS,ORS,NR,NF,FILENAME,FNR)


【简单例子】
1. number operations
int log sqrt exp sin cos atan2 rand srand ...

$cat rand.awk
BEGIN {
while(i<1000)
{
	n = int(rand()*100);
	rnd[n]++;
	i++;
}
for(i=0;i<=100;i++) {
	print i,"Occured", rnd[i], "times";
}
}
$

2. string operations
index length match split sprintf sub gsub gensub substr tolower toupper

[root@pandaVM script]# awk 'BEGIN{str="daabaaa" ;sub(/a/,"c&c",str) ;print str}'
dcacabaaa

3. input output operations
close fflush system

[root@pandaVM script]# awk 'BEGIN{print date}'
[root@pandaVM script]# awk 'BEGIN{system("date")}'
Tue Oct 21 10:40:16 CST 2014

4. if statement

$ awk '{
if ($3 >=35 && $4 >= 35 && $5 >= 35)
	print $0,"=>","Pass";
else
	print $0,"=>","Fail";
}' student-marks
Jones 2143 78 84 77 => Pass
Gondrol 2321 56 58 45 => Pass
RinRao 2122 38 37 => Fail
Edwin 2537 87 97 95 => Pass
Dayan 2415 30 47 => Fail

5. for loop ,break continue

$ awk 'BEGIN{
count=1;
do
print "This gets printed at least once";
while(count!=1)
}'
This gets printed at least once

6. build-in variables
FS - Input field separator variable.
OFS -  Output Field Separator Variable
RS - Record Separator variable
ORS - Output Record Separator Variable
NR - Number of Records Variable
NF - Number of Fields in a record
FILENAME - Name of the current input file
FNR - Number of Records relative to the current input file

$ awk -F':' 'BEGIN{OFS="=";} {print $3,$4;}' /etc/passwd
41=41
100=101
101=102
103=7
105=111
110=116
111=117
112=119

【参考链接】
http://www.thegeekstuff.com/tag/awk-tutorial-examples/
http://www.math.utah.edu/docs/info/gawk_13.html